In recent years, as people's living standard rises, they have a growing demand on food's color, scent and taste. Good smell is one of the characteristics of food. However, the scent of some foods can not last long. Hence, fragrance or flavor needs to be incorporated in the course of food processing to augment the food's aroma. Nonetheless, fragrance and flavor obtained by extraction and refining often have such disadvantages as easy evaporation, poor storability, etc. In allusion to this problem, if fragrance and flavor are microcapsulated, the following advantages may be achieved: healthfulness, economy, performance stability, uniform scent, good storability, convenient use, etc. In the United States, powder flavor made by microcapsulation technology accounts for more than 50% of the food fragrance. Powder flavor is now widely used in cakes, solid beverage, solid soup, fast food and leisure food, such as baked products, confection products, soup powder, and the like. Particularly for baking occurring in high temperature environment which tends to damage or evaporate flavor, microcapsulation can reduce loss of flavor to a great extent.
However, the performance of these microcapsulated fragrance products can't fully meet people's requirements yet. For example, Ding Lizhong, et al elaborated the release mechanism of a microcapsule in “Development of Research on Microcapsulation of Food Flavor” published on China Condiment, No. 2, pp. 90-95, 2009. In the processing of baked food, flavor experiences a high temperature above 80° C. A conventional liposoluble wall material, a glycerin ester, melts prematurely during baking due to its low melting point (generally below 60° C.), leading to release of the embedded flavor. As such, loss of flavor is still noticeable notwithstanding its release is somewhat retarded by the wall of the microcapsule. Research and development are continued in an attempt to find wall materials for microcapsules to obtain more ideal slow release performance.
High purity fatty acid mono- and di-esters of erythritol are good wall materials for microcapsules, because they have relatively high melting points (about 80° C.) and thus can achieve better protection and slow-release of flavor embedded therein. Preparation of these two compounds via biocatalysis is known in the art. For example, Junkui Piao, et al disclosed in particular the synthesis of erythritol α-monooleate and erythritol 1,4-dioleate by enzymatic catalysis in a paper titled “Synthesis of Mono- and Di-oleoyl Erythritols through Immobilized-lipase-catalyzed Condensation of Erythritol and Oleic Acid in Acetone” and published on Biochemical Engineering Journal, Vol. 14, No. 2, pp. 79-84, May 2003. Up to date, preparation of high purity mono- and di-ester products of erythritol by a chemical esterification process rather than enzymatic catalysis has not been disclosed by any references in the art. For example, Chinese Patent Application CN1649664A mentioned use of fatty acid esters or polyesters of erythritol in applications such as cosmetics, etc, wherein tin chloride was used as a catalyst, and diester, triester and tetraester in the resulting products had similar proportions. This mixture of mono- to tetra-esters has a significantly lowered melting point, and has no remarkable comparative advantages over conventional glycerin esters. Therefore, a need exists for development of a new process for preparation of high purity mono- and di-esters of erythritol, which can realize high product selectivity as well as simplified process and reduced cost.